1. Field of the Invention
The present invention relates to a manufacturing method and an optical information recording medium, and more specifically relates to a multilayer manufacturing method and a multilayer optical information recording medium.
2. Description of the Prior Art
In recent years, various types of optical information recording technology have been studied. According to the optical information recording, high density recording and non-contact recording/reproduction can be realized at a low cost. The method therefore has begun to be applied to various technical fields. An optical disk is used as a medium for the optical information recording. Optical disks are roughly classified into three types: read-only type; additional written type; and rewritable type. All the types of optical disks are commercialized and widely distributed. For example, the read-only type disk is distributed as a disk called as a compact disk (CD) on which music data is recorded or a laser disk (LD) on which image data is recorded. The additional written type disk is used for a document file or a still picture file. The rewritable type disk is used for a data file for a personal computer, or the like. The optical disk is formed in a structure in which an information recording layer is formed on a transparent resin substrate having a thickness of 1.2 mm and covered with an overcoat layer, or a structure in which an information recording layer is formed on one side or both sides of a transparent resin substrate having a thickness of 1.2 mm and the two substrates are bonded to each other.
In addition thereto, a digital versatile disk (DVD) having a larger capacity has been developed and commercialized to record not only audio data, but also video data such as a movie, and has begun to be popularized. In order to realize a high-density optical disk, a laser light beam having a short wavelength and an objective lens having a large numerical aperture (NA) are used. With use of the laser light beam having a short wavelength and the objective lens having a large NA, however, the tolerance of the inclination angle (tilt) of the disk to the incident direction of the laser beam will be decreased. In order to increase the tolerance of the tilt of the disk, it is effective to decrease the substrate in thickness. For example, in a DVD, the laser beam of the wavelength of 650 nm, and NA of 0.60, and the disk of the thickness of 0.6 mm are used. The resin substrate of 0.6 mm thick has poor mechanical strength and generates a tilt, and thus the DVD is formed by bonding two substrates to each other such that information recording face thereof is inside.
On the other hand, xe2x80x9ca one side face reproduction and double layer DVDxe2x80x9d has been also put into practical use, in which one substrate having a transparent reflective layer formed of gold, silicon, or the like on the information recording face and another substrate having a reflective layer formed of aluminum or the like on the information recording face are bonded each other such that the information recording faces thereof are bonded each other. For that DVD, the data on the information recording faces are reproduced by emitting a laser beam from the substrate side provided with the transparent reflective layer. Also, a rewritable DVD having the double layer structure as mentioned above in which a rewritable thin film recording layer is formed on the information recording face instead of a metal reflective layer, is also proposed.
Recently, the amount of the information grows larger as exemplarily seen in high definition television broadcasting, and therefore, the recording medium having high density is further required . In order to increase the recording density of the optical disk, various methods have been proposed: forming of the disk having a multilayer structure of more than three layers; increasing the NA of the objective lens; and using a blue-violet laser beam. As the method of forming the multilayer structure, a signal transferring (2P method) using a metal stamper has been widely used.
When the optical disk is formed to the multilayer structure, however, it is difficult to form an information recording face other than that having a groove or asperity pits formed by injection molding. It is proposed to decrease the recording/reproducing substrate in thickness and set the NA at 0.85, and the wavelength of the laser beam at 400 nm because the thinner the recording/reproducing substrate the larger the tolerance of the tilt of the disk, as described before. In a case where the recording/reproducing substrate is formed thinner than 0.3 mm that is the limit to form the groove or pits by the injection molding, the double layer structure cannot be easily formed. Also with use of the metal stamper, some problems will occur because a radiation cured resin film for transferring a signal recording face onto the disk cannot be easily formed uniformly, a radiation cured resin film cannot be formed uniformly and the radiation can not pass easily through the stamper. There are also some problems such that the radiation cured resin cannot be easily cured, a disk manufacturing apparatus is inevitably formed large, and signal transferring requires a long time.
The present invention intends to provide a manufacturing method of an optical information recording medium and an optical information recording medium having a multilayer structure, and more specifically, the optical information recording medium having a multi optical information recording layer and a thinner recording/reproducing substrate.
In a first aspect of the invention, provided is a method of manufacturing an optical information recording medium. The method comprises bonding a stamper having a principal plane formed with a groove or asperity pits and a second substrate having a thickness of 0.3 mm or less with radiation cured resin so as to cause the groove or the asperity pits to face to the second substrate, the stamper being transparent, the groove or asperity pits having a thin film formed thereon, curing the radiation cured resin, peeling off the stamper to form the groove or the asperity pits on the second substrate, forming a metal film or a recording film on the groove or the asperity pits on the second substrate to create a second information recording layer on the second substrate, and bonding a first substrate and the second substrate on which the second information recording layer is formed, such that the information recording layers are placed between the first and second substrates.
According to the above-mentioned manufacturing method, the optical disk having information recording layers can be formed on the substrate having a thickness of 0.3 mm or less which cannot be formed by the injection molding. Further, when the first substrate is provided with an information recording layer, the optical disk having a double layer structure can be attained.
According to the above-mentioned first manufacturing method, the stamper may be formed by injection molding. With this method, the disk can be formed at a low cost by the conventional optical disk manufacturing apparatus.
Preferably the stamper may be made of resin material, and more specifically, polycarbonate. With this method, a light and low-cost stamper can be attained. With this stamper, the radiation cured resin can be uniformly spread by spinning after overlapping the stamper and the first substrate by the radiation cured resin.
In the above-mentioned method, a metal film or a semimetal film may be formed on the information recording layer of the stamper. With this method, the stamper can be easily peeled off the first substrate.
The metal film may be formed from Al or metal mainly composed of Al. Thus, the stamper can be easily peeled off at a low cost. Further, the semimetal film of the information recording layer of the stamper may be formed from Si (silicon) or metal mainly composed of Si, and the manufacturing at lower cost can be attained.
In the above-mentioned first manufacturing method, the thin film may be applied with release agent thereon. With this method, the stamper can be more easily peeled off.
According to the above-mentioned first manufacturing method, the thickness of the second substrate may be substantially 0.1 mm. With this constitution, especially, when the objective lens of the pick-up has a large N.A., the high density optical disk can have the tilt margin equal to the conventional DVD.
In the above-mentioned first manufacturing method, the thickness at a clamp portion after the first substrate and the second substrate are bonded each other may be substantially 1.2 mm. With this constitution, compatibility to the conventional DVD and CD in a thickness of the clamp portion can be attained.
In the above-mentioned first manufacturing method, the thickness of the stamper may be substantially equal to that of the first substrate. With this constitution, both the stamper and the first substrate can be manufactured by substantially the same apparatus.
In the above-mentioned first manufacturing method, the center holes of the stamper and the second substrate may have different diameters. With this constitution, the stamper can be easily peeled off the first substrate.
In the above-mentioned first manufacturing method, each of the stamper and the second substrate may be different in outer diameter. With this constitution, the stamper can be easily peeled off the first substrate.
In the above-mentioned first manufacturing method, the second substrate having the information recording layer may be bonded with a supporting substrate on a face opposite to the face on which the information recording layer is formed, and a reflective film or a recording film is deposited on the information recording layer. With this constitution, the strength of the stamper having a thickness as thin as 0.3 mm or less can be increased to help the handling and film-forming.
In the above-mentioned first manufacturing method, it is preferable that a sum of thicknesses of the second substrate and the supporting substrate is substantially equal to that of the stamper or the first substrate. With this constitution, the manufacturing can be performed by substantially the same apparatus used for the film deposition of the stamper or the first substrate.
In a second aspect of the invention, provided is a method of manufacturing an optical information recording medium. The method comprises bonding a stamper having a principal plane formed with a groove or asperity pits and a first substrate having a first information recording layer with radiation cured resin so as to cause the groove or the asperity pits to face to the first information recording layer, the stamper being transparent, curing the radiation cured resin, peeling off the stamper to form the groove or the asperity pits on the first information recording layer of the first substrate, forming a metal film or a recording film over the groove or the asperity pits on the first substrate to create a second information recording layer on the first substrate, and forming a light transmission layer over the second information recording layer.
This method can produce an optical disk having plural information recording layers. The stamper is formed of light and flexible resin, and thus can be easily handled. Therefore, the radiation cured resin for transmitting signal pits can be spread substantially uniformly on the substrate by rotating the substrate with the spin-coating. The stamper can be easily handled and formed in mass production at a low manufacturing cost in comparison with the metal stamper.
In the above-mentioned second manufacturing method, the thickness of the light transmission layer may be 0.3 mm or less. With this structure, the NA of the recording/reproducing optical system can be easily increased, thereby the recording density of the optical disk can be increased.
In the above-mentioned second manufacturing method, the thickness of the light transmission layer may be substantially 0.1 mm. With this structure, the optical disk can maintain the tilt margin equal to that of the DVD even if the NA of the recording/reproducing optical system is increased to around 0.9.
In the above-mentioned second manufacturing method, the light transmission layer may be formed of radiation cured resin. By forming the layer in this manner, the layer can be manufactured at a low cost.
In the above-mentioned second manufacturing method, the light transmission layer may be formed by bonding the first and second substrates. By forming the layer in this manner, the variety of the light transmission layer can be suppressed.
In the above-mentioned second manufacturing method, the stamper may be formed by injection molding. With this method, the disk can be formed at a low cost by the conventional optical disk manufacturing apparatus.
In the above-mentioned second manufacturing method, the stamper may be formed from resin material, and more specifically, polycarbonate.
By forming the stamper from polycarbonate, a light and low-cost stamper can be attained. With this stamper, the radiation cured resin can be uniformly spread by spinning after overlapping the stamper and the first substrate by the radiation cured resin.
Further, the first substrate and the stamper are bonded in a vacuum, and no bubbles may be inserted.
In the above-mentioned second manufacturing method, the thin film may be applied with release agent thereon. With this method, the stamper can be more easily peeled off, and the transferring of the groove and the pits can be improved.
In the above-mentioned second manufacturing method, a thin film may be formed on the groove or asperity pits of the stamper. By forming the thin film, the stamper can be more easily peeled off.
In the above-mentioned second manufacturing method, the thin film may be a metal film or a dielectric film. With this method, if the Si is used as the metal, the manufacturing at lower cost can be attained. Further, the thin film is applied with release agent, and thus the stamper can be more easily peeled off.
In the above-mentioned second manufacturing method, radiation may be emitted substantially parallel to the principal plane of the stamper when the radiation cured resin is cured after the stamper and the first substrate are integrated by the radiation cured resin. With this method, the radiation cured resin can be cured even if the stamper and the first substrate have principal planes with poor radiation transmittance.
In the above-mentioned second manufacturing method, the thickness at a clamp portion may be substantially 1.2 mm. With this constitution, the interchangeability to the conventional DVD and CD in the thickness of the claim portion can be attained.
In the above-mentioned second manufacturing method, the thickness of the stamper may be substantially equal to that of the first substrate. With this constitution, both the stamper and the first substrate can be manufactured by substantially the same apparatus.
In the above-mentioned second manufacturing method, the center holes of the stamper and the first substrate may have substantially the same diameter. With this constitution, the center of the groove or asperity pits of the stamper can be aligned to the center of the signal recording layer of the first substrate by aligning the center holes.
In the above-mentioned second manufacturing method, it is preferable that each of the stamper and the first substrate are different in outer diameter. With this constitution, the stamper can be easily peeled off the first substrate.
In the third aspect of the invention, provided is a method of manufacturing an optical information recording medium. The method comprises: applying first radiation cured resin onto a groove or asperity pits formed on a principal plane of a stamper; bonding the stamper and a first substrate having a principal plane on which a first information recording layer is formed with second radiation cured resin such that the first radiation cured resin and the first information recording layer face each other, and curing the second radiation cured resin; peeling off the stamper to form a groove or asperity pits made of the first radiation cured resin on the first substrate; and forming a reflective film or a recording film on the groove or the asperity pits on the first substrate to make a second information recording layer.
With this method, the multilayered optical disk can be easily formed even if the disk has a thin recording/reproducing side substrate. Since the stamper is formed of light and flexible resin, it can be easily handled. Therefore, the radiation cured resin for transmitting signal pits can be spread substantially uniformly on the substrate by rotating the substrate with the use of the spin-coating. The stamper can be easily handled and formed in mass production at a low manufacturing cost in comparing with the metal stamper.
In the fourth aspect of the invention, provided is a method of manufacturing an optical information recording medium. The method comprises: applying second radiation cured resin onto a first information recording layer formed on a principal plane of a first substrate, and curing the second resin; bonding a stamper having a principal plane formed with a groove or asperity pits and the first substrate with first radiation cured resin such that the groove or asperity pits and the second resin face each other, and curing the first radiation cured resin; peeling off the stamper to form groove or asperity pits made of the first radiation cured resin on the first substrate; and forming a reflective film or a recording film on the groove or the asperity pits on the first substrate to make a second information recording layer.
With this manufacturing method, equivalent advantages to those described for the first method can be attained.
In the fifth aspect of the invention, provided is a method of manufacturing an optical information recording medium. The method comprises: applying first radiation cured resin onto a groove or asperity pits formed on a principal plane of a stamper; applying second radiation cured resin onto a first information recording layer formed on a principal plane of a first substrate; bonding the stamper and the first substrate such that the first radiation cured resin and the second radiation cured resin face each other, and curing the first and second radiation cured resin; peeling off the stamper to form a groove or asperity pits made of the first radiation cured resin on the first substrate; and forming a reflective film or a recording film over the groove or the asperity pits on the first substrate to form a second information recording layer.
With this manufacturing method, equivalent advantages to those described for the first method can be attained.
In the sixth aspect of the invention, provided is a method of manufacturing an optical information recording medium. The method comprises: forming a first thin film comprising at least one layer on a groove or asperity pits formed on a principal plane of a stamper; forming a second thin film comprising at least one layer over the first thin film; bonding the stamper and a first substrate having a principal plane on which a first information recording layer is formed with radiation cured resin such that the second thin film and the first information recording layer face each other; peeling off the stamper and the first substrate at an interface of the first and second thin films to form a groove or asperity pits made of the second thin film on the first substrate; and forming a reflective film or recording film on the groove or the asperity pits on the first substrate to form a second information recording layer.
In the above-mentioned the third to sixth manufacturing methods, third radiation cured resin may be applied on the first information recording layer SA of the first substrate in advance, and the third radiation cured resin HC is cured. In this manner, the first information recording layer SA can be prevented from being damaged when the stamper is peeled off. Especially, this is more effective for a case where the first information recording layer SA is a rewritable recording layer comprising a plurality of thin films, since the thin films may have poor strength. The advantage of protecting the first information recording layer SA from deterioration such as corrosion can also be attained.
Further, the third radiation cured resin may have a pencil hardness of B or more. The first information recording layer SA can be thereby prevented from being damaged. The third radiation cured resin HC also may be applied at least from an inner peripheral edge to an outer peripheral edge of the first information recording layer. By applying the resin HC in this manner, the resin HC can function effectively.
In the above-mentioned third to sixth manufacturing methods, a light transmission layer may be formed on the second information recording layer SB. By forming this layer, the second information recording layer SB can be protected. The thickness of the light transmission layer may be 0.3 mm or less. By forming the layer so thick, the wavelength of the light emitted from the recording/reproducing optical system can be shortened, and the NA can be easily increased. Further, the optical disk having information recording layers can be formed on the substrate having a thickness of 0.3 mm or less which cannot be formed by injection molding, and the optical disk having high density can be attained.
Further, the thickness of the light transmission layer may be substantially 0.1 mm. With this structure, the optical disk can maintain the tilt margin equal to that of the DVD even if the NA of the recording/reproducing optical system is increased to around 0.9. Also, the light transmission layer may be formed of radiation cured resin. With this method, the disk can be formed at a low cost. Further, the light transmission layer may be formed of radiation cured resin and a resin substrate. By forming the layer in this manner, the variety of the light transmission layer in thickness can be suppressed, and the layer can be easily formed.
In the above-mentioned the third to fifth manufacturing methods, it is preferable that the stamper transmits at least one of radiations having wavelengths for curing the first or second radiation cured resin LA or LB. In the above-mentioned the fourth manufacturing method, the stamper and the first and second thin films FA and FB may transmit at least one of radiations having wavelengths for curing the first or second radiation cured resin. With this method, the first radiation cured resin LA, the second radiation cured resin LB, or the radiation cured resin can be cured even if radiation cannot transmit through the first substrate or the information recording layer SA.
In the above-mentioned the third to fifth manufacturing methods, the stamper may be formed from resin material. The stamper is formed of light and flexible resin in comparison with the metal stamper. Therefore, the radiation cured resin for transmitting signal pits can be spread substantially uniformly on the substrate by rotating the substrate with use of the spin-coating employed for DVD manufacturing, not by applying a high pressure as in the 2P method employed for the metal stamper or taking a long period of time, and can be easily handled. The stamper can be easily handled and formed in mass production by the injection molding at a low manufacturing cost in comparison with the metal stamper. It is difficult to prepare a lot of spare metal stampers, and thus the replacing of the stamper is troublesome.
The stamper may be formed by injection molding. With this method, the disk can be formed at a low cost by the conventional optical disk manufacturing apparatus. The stamper may be formed mainly of polycarbonate. With this method, the disk can be formed by the conventional optical disk manufacturing apparatus.
In the above-mentioned the third, fourth, and sixth manufacturing methods, the radiation cured resin may be spread by spinning after overlapping the stamper and the first substrate by the radiation cured resin in order to uniformly spread the radiation cured resin. By forming the stamper from resin material, a light and low-cost stamper can be attained. With this method, the disk can be formed by the conventional manufacturing apparatus employed for adhesion of the DVD. Further, the first substrate and the stamper may be bonded in a vacuum, and thus no bubbles may be inserted. In addition, the radiation cured resin and the stamper can be stuck more strongly, and the transferability can be improved.
In the above-mentioned the third manufacturing method, an inner diameter of the first radiation cured resin LA may be smaller than an inner diameter of the second radiation cured resin LB. By applying resin in this manner, the second radiation cured resin LB will not adhere to the stamper in the inner peripheral portion, and thus the stamper can be easily peeled off the first substrate.
In the above-mentioned third and fifth manufacturing methods, the first radiation cured resin LA may be applied toward an outer peripheral edge of the stamper. By applying resin in this manner, the second radiation cured resin LB will be prevented from contacting with the stamper in the inner peripheral portion, and thus the stamper can be easily peeled off the first substrate.
In the above-mentioned fourth manufacturing method, an inner diameter of the second radiation cured resin LB is smaller than an inner diameter of the first radiation cured resin LA. By applying resin in this manner, the first radiation cured resin LA will not adhere to the first substrate in the inner peripheral portion, and thus the stamper can be easily peeled off the first substrate.
In the above-mentioned fourth and fifth manufacturing methods, the second radiation cured resin LB is applied toward an outer peripheral edge of the first substrate. By applying resin in this manner, the first radiation cured resin LA will not adhere to the first substrate in the inner peripheral portion, and thus the stamper can be easily peeled off the first substrate.
In the above-mentioned sixth manufacturing method, inner diameters of the thin first and second thin films FA and FB may be smaller than an inner diameter of the radiation cured resin. By forming the thin films in this manner, the radiation cured resin will be prevented from adhering to the first substrate in the inner peripheral portion, and thus the stamper can be easily peeled off the first substrate.
In the above-mentioned sixth manufacturing method, the thin first and second thin films FA and FB may be formed to cover an outer peripheral edge of the stamper. By forming the thin films in this manner, the radiation cured resin will be prevented from adhering to the first substrate in the outer peripheral portion, and thus the stamper can be easily peeled off the first substrate.
In the above-mentioned third to fifth manufacturing methods, the groove or the asperity pits of the stamper may be subjected to a process for facilitating the peeling of the stamper. With this method, the stamper can be more easily peeled off, and the transferring can be improved. The groove or the asperity pits of the stamper may be applied with release agent. With this method, the stamper can be more easily peeled off, and the transferring can be improved. A film mainly formed from metal may be formed on the groove or the asperity pits of the stamper. With this method, the stamper can be more easily peeled off, and the transferring can be improved.
In the above-mentioned the sixth manufacturing method, the first thin film FA may be formed of Au and the second thin film FB may be formed of SiO2. With this method, the stamper can be more easily peeled off.
In the above-mentioned third to sixth manufacturing methods, center holes of the stamper and the first substrate may be substantially equal to each other in diameter. With these center holes, centers of a plurality of information recording layers formed on the first substrate can be aligned with ease.
With use of the optical information recording medium manufactured according to the above-mentioned third to sixth manufacturing methods, high-density recording using a plurality of information recording layers can be attained.
In the seventh aspect of the invention, provided is an optical information recording medium having a substrate. The medium comprises: an information recording layer formed on the substrate; at least one basic layer which is stacked on the information layer, and includes an intermediate layer and a recording layer; and a light transmission layer formed on the basic layer. With the optical information recording medium of the present invention, high-density recording using a plurality of information recording layers can be attained. Further, the protection layer and the light transmission layer protect the information recording layers, and thus stable manufacturing can be secured. The medium is also advantageous in being manufactured by the above-mentioned first, second, third, and fourth manufacturing methods with ease.
In the medium, the thickness of the light transmission layer may be 0.3 mm or less. By forming the layer so thick, the wavelength of the light emitted from the recording/reproducing optical system can be shortened, and NA can be easily increased, thereby the recording density of the optical recoding medium can be increased. Further, the thickness of the light transmission layer may be substantially 0.1 mm. With this structure, the optical disk can maintain the tilt margin equal to that of the DVD even if the wavelength of the recording/reproducing light beam is shortened to around 400 nm and the NA of the recording/reproducing optical system is increased to around 0.9. The thickness of the basic layer may be not less than 15 xcexcm and not more than 45 xcexcm when the thickness of the light transmission layer is substantially 0.1 mm. By setting the thickness in this manner, the influence of the interference of reproduction signals of a plurality of optical recording media and the influence of the recording light can be suppressed. Further, the recording/reproducing with use of the lens having the high NA can be easily prevented from being influenced by spherical aberration or the like.
Further, the light transmission layer may be formed of radiation cured resin. With this method, the disk can be securely formed at a low cost, and the variety of the light transmission layer in thickness can be suppressed, and the layer can be formed uniformly. Further, the light transmission layer may be formed of radiation cured resin and a resin substrate. By forming the layer in this manner, the variety of the light transmission layer can be suppressed, and the layer can be easily formed.
The recording layer may comprise radiation cured resin having the groove or the asperity pits, and a reflective film or a recording film formed on the groove or the asperity pits. With this structure, the high-density recording medium comprising a plurality of information recording layers can be attained. Using radiation cured resin, the manufacturing can be performed with ease at a low cost.
The intermediate layer may have a function as adhesive. Thus, the optical information recording medium can be stabilized. The intermediate layer may be formed of radiation cured resin. Thus, the manufacturing can be performed with ease at a low cost.
The protection layer may have a pencil hardness B or more. By setting the hardness of the protection layer in this manner, the information recording layer can be protected from corrosion or shock, and damage applied to the information recording layer during the manufacturing can be also suppressed. The protection layer may be formed of radiation cured resin. Thus, the manufacturing can be performed with ease at a low cost.
The protection layer and the intermediate layer may have substantially equal refractive indexes. By setting the refractive indexes in this manner, the recording/reproducing light can stably perform the recording/reproducing without optical interference of spherical aberration. The protection layer and the intermediate layer may be substantially transparent to transmit recording/reproducing light. By employing such layers, the recording/reproducing light can stably perform the recording/reproducing without optical interference of absorption or dispersion.
The intermediate layer may be substantially transparent to transmit recording/reproducing light. By employing such a layer, the recording/reproducing light can stably perform the recording/reproducing without optical interference of absorption or dispersion.
In an eighth aspect of the invention, provided is an optical information recording medium comprising a first substrate, and a second substrate which is thinner than the first substrate. Two information recording layers are provided between the first and second substrates.
In a ninth aspect of the invention, provided is an optical information recording medium comprising a first substrate, and a light transmission layer which is provided on the first substrate and is made of radiation cured resin. Two information recording layers are provided between the first substrate and the light transmission layer.